How to manipulate a individual edge
If you want to merge the 2 edges, you should first enable the Auto-Merge option:

Then select both the 2 edges and CtrlE &gt; Bridge Edge Loops to bridge. Now select the top edge and slide it down with GG. You may not even need the bridge if the 2 edges are correctly aligned, in that case enable the Snap (Vertex mode) and the Auto-Merge options and move down the top edge.